This invention relates to wastewater treatment where levels of organic contaminants, such as phenols and related compounds, are to be decreased.
Several industrial processes require the use of large quantities of water for their operations. The water may come from natural sources such as rivers or from treated city water. As a consequence of the industrial activities, the used water may become contaminated with organic pollutants beyond permissible, environmentally acceptable limits.
Organic contaminants can be removed to a limited degree by adsorption on activated carbon, ozonation, or a combination of these methods. After use, activated carbon, if filled with contaminants, requires destruction or disposal to a special landfill. In addition, activated carbon is not necessarily selective enough to efficiently absorb the problem compounds, and when the active sites are full, the adsorption capacity goes down to zero. Ozone is a dangerous chemical and it would be preferred if its use could be avoided in wastewater treatment.
Electrochemical treatment of wastewater can reduce the level of organic contaminants by oxidation. Noding (U.S. Pat. No. 4,652,355) discloses an electrochemical reactor in which the anode and cathode in a reaction chamber are in the same plane as the direction of flow of aryl-containing wastewater. This reactor predominantly produces aryl hydroquinones, which are not ideal end products for environmental release.
Similarly, Cole (U.S. Pat. No. 5,531,865) discloses an electrochemical reactor having a cathode and a plurality of sacrificial anodes elongated in a chamber, parallel to the direction of flow of contaminated water. With such a configuration of electrodes, charge density will vary across the cross-section of the reaction chamber, and it is possible that a significant amount of aryl compounds will not contact an anode, and experience sufficient charge density to be oxidized, while flowing through the chamber.
Several patents have issued relating to reactors that, in attempting to optimize the possibility of electrochemical reaction, make available significant electrode surface area by having multiple solid electrodes in various configurations and/or requiring meandering flow of wastewater over the surface the electrodes (for example U.S. Pat. Nos. 5,549,812 (Witt); 5,587,057 (Metzler et al.); 5,611,907 (Herbst et al.); 5,746,904 (Lee); and 5,928,493 (Morkovsky et al.)). The reactors found in these patents tend to be of relatively complex construction and the flowpath of the wastewater over solid electrodes, in each case, does not guarantee intimate contact with an anode surface.
Sampson et al. (U.S. Pat. No. 5,705,050) discloses a packed bed reactor, which includes an ion exchange material packed between an anode and a cathode. However, ion exchange materials require special handling and specific reactor conditions to tolerate higher back pressures that can occur.
By using at least one porous anode, the electrochemical reactor of the present invention addresses limitations in known reactors. By directing the flow of wastewater through the pores of at least one porous anode, the reactor disclosed herein provides a high probability that contaminant molecules will experience intimate contact with an anode and thus encounter the necessary current density for oxidation. This advantage is coupled with the relatively simple construction of the reactor and ease of maintenance.
The invention provides an electrochemical reactor (cell) for reducing the concentration of organic compounds, such as aryl compounds, found in wastewater from industrial processes. Breakdown of the organic compounds occurs by oxidation at the anode of the electrochemical reactor.
More specifically, the present invention provides a flow-through electrochemical reactor comprising:
a body having an internal chamber, and an inlet port and an outlet port in communication with said internal chamber to permit flow of wastewater therethrough;
at least one porous anode arranged in said internal chamber such that the wastewater flowing between said inlet port and said outlet port flows through the pores of said at least one porous anode, said at least one porous anode having activity for the destruction of a target substance; and
at least one cathode disposed in the internal chamber to permit an electric current to be established between said at least one cathode and said at least one anode, said electric current reducing the concentration of said target substance in the wastewater flowing through the chamber.
The reactor, when in use, reduces TOC content of industrial wastewater by oxidizing target substances, such as aryl compounds, efficiently. Efficient oxidation minimizes the possibility of competing side reactions. The side reactions are unfavorable since they might produce compounds that are as harmful as, or more harmful than, the compounds to be destroyed.
Thus, the electrochemical reactor can treat a wastewater stream to reduce the concentration of aryl compounds to an environmentally acceptable level. The reactor of the present invention also offers the advantage that it can be installed within an existing piping system.